Actors appreciate a smart script, too, but they also say the 50-year-old film geek is a good director. We've pulled some insight on his directing from "Joss Whedon: The Biography" by Amy Pascale, which comes out on August 1.

It starts with Whedon's confidence and ability to inspire confidence in others.

On the start of "Buffy," the director assured actor Anthony Stewart Head that, though network suits wouldn't appreciate the show, it would by word of mouth develop a worldwide fanbase. “He’s certain of his beliefs. He sticks to them. He doesn’t waver,” Head told Pascale.

Beyond writing good scripts, Whedon is willing to adapt scripts on the fly based on feedback and new ideas. This fosters a “collaborative spirit across the whole cast and the whole crew that kept everything running very smoothly," producer Kevin Feige told Pascale. Not surprisingly, Whedon's ideas tend to win out.

“When Joss directs, he has a way of saying no that you don’t care that your idea was rejected,” actor Nathan Fillion told Pascale. “ ‘I have an idea. What if I do it like this, and I jump around and I take my time, and do a little—,’ and he says, ‘Oh, that’s a great idea. Or . . .’ His idea is so much better, realistic, and clever. And then, I go, ‘Oh my God, that’s brilliant, yes! Yes, of course that’s how I should do it.’"

Whedon takes time to develop characters with actors, which was key to getting so many to fit together on "The Avengers."

He is apparently a good actor and knows how to give good guidance to actors.

"Stanley [Kubrick] was not as good a communicator with actors as Joss is," actor Adam Baldwin, who worked with both directors, told Pascale. "Stanley would just have you do it again and yell at you that you were lame and bad and need to be a better actor, whereas Joss would say, ‘Well, try this’ or ‘Try that,’ and he would care."

“Joss came to my rescue on many occasions to get me in the right spot," actor Mark Ruffalo told Pascale. “A lot of directors don’t; they can give you ideas, and they explain it to you, but that doesn’t necessarily mean that what they’re telling you is actable, and a lot of times you’ve got to translate what the director’s saying into making that actable."